Add module APIs for custom authentication

Add configuration option for allowing reads on cluster down

Fix outdated information on max memory policies

init server.hz early to avoid div by 0 during config file loading

Improve RM_ModuleTypeReplaceValue() API.

With the previous API, a NULL return value was ambiguous and could
represent either an old value of NULL or an error condition. The new API
returns a status code and allows the old value to be returned
by-reference.

This commit also includes test coverage based on
tests/modules/datatype.c which did not exist at the time of the original
commit.

since the refactory of config.c, it was initialized from config_hz in initServer
but apparently that's too late since the config file loading creates objects
which call LRU_CLOCK

Add no-slowlog to acl command to prevent passwords

Omits  `ACL SETUSER` from redis-cli's history

Modules must have execute permissions to load

fix leak in RM_LoadDataTypeFromString, and save

This message is there for ten years, but is hardly useful.
Moreover it is likely that it will fill an entire disk if log ratation
is not configured, for no good reasons.

Add ULL suffix to CLIENT_TRACKING flag to prevent sign extension

the code in:
        c->flags &= ~(CLIENT_TRACKING|CLIENT_TRACKING_BROKEN_REDIR);
will do sign extension and turn on all the high 31 bits
no damage so far since we don't have any yet

Fix memcpy of id from key to be slightly safer.

+        memcpy(&id,ri.key,sizeof(id));

The memcpy from the key to the id reliease on the fact that this key
*should* be 8 bytes long as it was entered as such a few lines up the
code.

BUT if someone will change the code to the point this is no longer true,
current code can trash the stack which makes debugging very hard
while this fix will result in some garbage id, or even page fault.
Both are preferable to stack mangaling.